Conventionally, electronic circuits on a substrate are implemented by using a packaged (resin sealed) ICs and microcomputers because of their ease of handling and resistivity to environmental influence. However, demand for high functionality and more complicated system in electronic control units (ECUs) urges increase of the scale of the electronic circuits, in spite of a limited space reserved for the ECUs.
The limitation imposed on the ECUs drives reduction in volume of the electronic circuits by using smaller ICs (packaged parts, chip-size packages, bare chips [IC chips without resin seal] or the like). In this case, reduced spacing between the terminals and/or decreased size of the terminals on the smaller ICs make it more difficult to perform quality inspection by contacting the terminals.
Japanese Patent Document JP-A-H5-72280 discloses an electronic circuit inspection method for quality assurance that inspects the electronic circuits in a state of implementation on a board. However, the electronic circuit implemented on the board has peripheral circuits connected thereto, thereby receiving influence from the peripheral circuits during inspection and having inaccuracy in inspection result. That is, critical inspections in terms of product quality such as leakage current inspection, function inspection or the like cannot be performed on the electronic circuit in the state of implementation on the board.